A valid circle has radius larger than 0.0 and a base plane which is must also be valid.

Namespace: Rhino.Geometry
Assembly: RhinoCommon (in RhinoCommon.dll) Version: Rhino 6.0

C#

public bool IsValid { get; }

VB

Public ReadOnly Property IsValid As Boolean
	Get

Type: Boolean

Supported in: 6.0.16224.21491, 5D58w

Circle Structure
Rhino.Geometry Namespace